This invention relates to an altitude computer which is adapted to supply a rate of change in altitude indicator with information to enable a pilot to safely operate an aircraft.
Most present day aircraft use air data computers to calculate information utilized in piloting an aircraft. These air data computers receive information relating to pressure data, indicated air speed, rate of ascent or descent and temperature in order to calculate true air speed and density altitude. The rate of climb and descent information is especially useful during take-off and landings in order that a pilot can provide a smooth transition of the aircraft into the flight pattern around airports.
Information relating to rate of ascent and descent is usually derived from a rate sensing apparatus associated with the altitude sensing aneroid of the type disclosed in U.S. Pat. No. 3,456,506. Such rate sensing apparatus include a hollow diaphragm or aneroid located in a sealed container. The interior of the diaphragm is vented to the surrounding environment. However, a flow restricting orifice limits communication between the sealed container and the surrounding environment. Any change in atmospheric pressure due to a change in altitude of the aircraft is immediately communicated to the interior of the diaphragm; however, the flow restricting orifice delays the change in atmospheric pressure communicated into the sealed container and thereby creates a pressure differential across the diaphragm. This pressure differential causes the diaphragm to expand or contract depending upon whether the aircraft is ascending or descending. A mechanical linkage connects the diaphragm to an indicator dial to provide the pilot with rate of change in altitude information. It has recently been discovered that the relationship between atmospheric pressure and altitude is only linear up to about 28,000 feet. Therefore, the accuracy of differential pressure rate sensing apparatus is limited to altitudes below 28,000 feet.